	<!DOCTYPE html>
	<html>
		<head>
			<meta charset="utf-8" />
			<meta name="viewport" content="width=device-width, initial-scale=1">
			<title>Title</title>
		</head>
		<body>
			<input type="button" name="" id="btn" value="呵呵" />
			<input type="text" name="" id="txt" value="洋酒" />
			
			<script src="jquery-1.12.4.js" type="text/javascript" charset="utf-8"></script>
			<script type="text/javascript">
				$(function(){
// 					console.log($("#btn").val());
// 					$("#btn").val("哈哈");
// 					console.log($("#btn").attr("value"));
// 					
// 					$("#txt").val("123");
// 					console.log($("#txt").val());
						$("#txt").focus(function(){
							//如果是默认值,清空内容
							if($(this).val() === "洋酒"){
								$(this).val("");
							}
						});
						$("#txt").blur(function(){
							if($(this).val() === ""){
								$(this).val("洋酒");
							}
						});
				});
			</script>
		</body>
	</html>